The objective of this research project is to understand how the retina of mammals analyzes the visual world and encodes its spatial, temporal and chromatic contrast into a message of action potentials for safe sending to the brain. It is proposed to investigate which chemical messages are converging upon each type of retinal neuron, the weight of these messages, their destination at the cell surface and their neuron of origin. Furthermore, if one were able to recognize in vitro, after retinal dissociation, the neuron that represents the target of such messenger molecules, one could correlate its wiring with the cell's physiology. One would also possess a strategy for designing critical physiological experiments and investigate the influence of the appropriate constellation of neuroactive substances on the ligand- and voltage-gated currents of the postsynaptic cell. Armed with this combined knowledge of structure and function, if one could identify morphologically the various species of receptors and ion channels expressed by each type of retinal neuron, one could perhaps predict the nature of the neural interactions at sites that are not accessible to physiological experimentation. Aim of this application, in addition to that of completing ongoing work on the bipolar cells of the rabbit, is to combine molecular biology with microscopy and electrophysiology in the study of the functional wiring of the mouse retina. Homogeneous populations of retinal neurons will be labeled by introducing into the mouse genome chimeric constructs consisting of a reporter gene and the promoters of genes whose products participate in visual processing. The reporter genes are (i) alkaline phosphatase that can be detected at both light and electron microscopes with simple and reliable techniques; (ii) beta-galactosidase that can be identified in living cells with a fluorescent dye. The promoters will be those that regulate transcription of genes coding for peptides, rate-limiting enzymes of transmitter metabolism, receptors and ion channels. The morphological parameters of the labeled cell populations will be studied as well as their synaptic connections. Furthermore, living cells that carry the reporter gene will be identified in vitro after dissociation of the retina: in this way, it will be possible to study the voltage- and ligand-gated currents of the retinal neurons that carry the transgene by means of the whole-cell patch clamp technique and integrate the data thus obtained into the neural networks that were described anatomically. These sort of studies are fundamental to the understanding and rational treatment of the disorders of the retina and nervous system in general.